We have all some experience of a feeling, that comes over us occasionally, of what we are saying and doing having been said and done before, in a remote time - of our having been surrounded, dim ages ago, by the same faces, objects, and circumstances - of our knowing perfectly what will be said next, as if we suddenly remember it!
It happens to me and it has probably happened to you. It is sudden and fleeting, leaving as unexpectedly as it came. While the experience is striking in its clarity and detail, it is difficult to recapture or recount. Generally, it is left unexplained and is described in a vague sense, often simply as, "Wow, I just got the strangest déjà vu." Because it is so difficult to research and seems to have no deleterious effects on daily and long-term nervous system function, déjà vu has been left largely to the wayside of neurobiological investigation. In all of its ambiguity, déjà vu is still a perplexing phenomenon that has not yet been fully explained. The value of truly understanding the source of déjà vu and its circuitry is in uncovering one of the many keys to the role of the conscious self in the functioning of the brain.
What is déjà vu and how does it work? Déjà vu is considered a common phenomenon. Surveys show that about one third of the population has had the most common form of déjà vu sensations. Due to the subjective and often indescribable nature of the associated feelings, it has been difficult, to determine who is actually experiencing déjà vu. In general, however, déjà vu is "any number of hard-to-explain sometimes upsetting occurrences of unexpected recognition, in which the person involved has trouble identifying an antecedent for the events and/or places which seem so strangely and intensely familiar." Déjà vu has been defined as "familiarity without awareness." While the situational cues of a déjà vu are familiar, there is a definite lack of awareness about the specific source of the memory.
There are three different types of Déjà vu. 1) Deja Senti: This feeling refers to something 'already felt'. It is a mental phenomenon and researchers believe that something felt in the past is very similar to that felt in the present. This similarity in the two experiences makes a person feel that he/she has felt the same way in the past. Deja Vecu: A feeling that everything that is happening currently is identical to what had happened before and a strange idea about what is going to happen next, is termed as Deja Vecu. A person experiencing a Deja vecu feeling claims to know what is going to happen in near future and often feels to have remembered it. Deja Visite: This form of Deja vu is a feeling of having visited a completely new place. A person experiencing this form of Deja vu claims to have knowledge of an unvisited place. One claims to be well aware of the geography of a place, when the person has never been there in reality. Deja Visite is characterized by a weird know-how of a spot one has never ever visited. Déjà vecu is the most common déjà vu experience and involves the sensation of having done something or having been in an identical situation before and knowing what will happen next. These sensations are often felt through several senses: seeing, hearing, taste, touch and proprioceptive perceptions. The experience is often incredibly detailed and is usually connected to very normal activities. Although the episode itself lasts from only a fraction of a second to several minutes, it can often be remembered in minute detail long after the episode has occurred. One experiencer says, "There came this strange, almost physical up-welling of visual experience, a visual warping, and at the same time an eerie realization that everything happening now had happened before, maybe many times."
Déjà senti is different from déjà vecu in that the episode of recollection feels more like the recovery of long sought after information. The sensation is one of satisfaction at having retrieved a memory although the memory was not actively sought. This form of déjà vu does not involve any feelings of premonition and the episodes quickly dissipate from memory. Déjà senti has been strongly associated with the partial seizure experiences reported by temporal lobe epilepsy patients. The extended nature of these episodes has allowed for more detailed descriptions of the feelings associated with a déjà senti event. "It was as if one of my dreams had simply been sucked out of the actual, physical environment and set to playing again in every detail." Déjà visité is a more rare event in which a person visits a new place and feels that it is familiar. It is associated more with spatial dimensions while déjà vecu is associated with situations and processes. Déjà vu experiences can be in one of the three forms described above or can be a mixed version with a combined déjà vu effect .
What causes a déjà vu episode? There are several possible explanations for what is occurring during a déjà vu experience. One possibility is simply the occasional mismatch made by the brain in its continuous attempt to create whole sensical pictures out of very small pieces of information. Looking at memory as a hologram, only bits of sensory information are needed for the brain to reconstruct entire three-dimensional images. When the brain receives a small sensory input (a sight, a smell, a sound) that is strikingly similar to such a detail experienced in the past, the entire memory image is brought forward. The brain has taken the past to be the present by virtue of one tiny bit of sensory information. It is this mismatch of past and present sensory information that causes the sense of disconcertment and unease associated with a passing déjà vu . This theory provides a satisfactory explanation for the physical effects of déjà vu. These appear to be similar to the effects of mismatch between sensory input and corollary discharge signal information to the brain. It does not, however, seem to provide sufficient answers to individual (even my own) accounts of déjà vu, where the memory image pulled up is not necessarily from a true past event.
Another explanation for déjà vu is that there is a slight malfunctioning between the long and short-term memory circuits of the brain. Somehow, specific information shortcuts its way from short to long-term memory storage, bypassing the usual mechanisms used for storage transfer. The details concerning this shortcut are not yet well understood. When this new, recent piece of information is drawn upon, the person thinks that the piece is coming from long-term storage and so must have come from the distant past . A similar theory says that the error is in the timing of the perceptive and cognitive processes. Sensory information is rerouted on its way to memory storage and, so, is not immediately perceived. This short delay causes the sensation of experiencing and remembering something at the same time, a very unsettling feeling . One other explanation is that déjà vu is actually the process of remembering memory connections, of following the impulses and synapses . All of these neurobiologically based explanations for déjà vu seem plausible and intriguing and perhaps there is some overlap or combination that accounts for the different experiences we call déjà vu.
Other explanations for déjà vu have been given by psychoanalysts, such as the manifestation of wish fulfillment. Here, déjà vu is the subconscious repetition of a past experience, but with a more positive ending . The realm of parapsychology proposes that déjà vu is a chance for reincarnates to get a sneak peak into a past life. Most scientists scoff at these "magical" explanations for neurological events, citing that they break many of the laws of nature . Some, however, point to more recent findings in physics, such as the possibility of particles that can travel backwards in time (tachyons), time loops and multiple universes. They say that these may give cause for more non-traditional ways of seeing causality and for the possibility of neurological "time travel" . This means that, maybe, just maybe, understanding déjà vu as a means of seeing into the past or future cannot be so immediately dismissed. It is certainly food for thought for the rising debate, anyway.
It is important to note the level of consciousness involved in a déjà vu episode. There are common threads that run through many déjà vu experiences. "When you are in the midst of such an occurrence, you are conscious that everything conforms with your 'memory' of it" and "I know exactly what is going on around me when it happens." This implies that the participation of the entire brain capacity is not required to produce a déjà vu experience. Perhaps more importantly, there is a significant role played by at least a portion of the conscious person and the I-function. "It was like being in a long-running play, complete with the sense of being 'on' and standing
What is this role of the self in déjà vu? "To what extent is it possible for the core awareness to preserve ... images and emotions before they're swallowed up again and sealed tight? " One epileptic déjà vu experiencer claimed that he could consciously recapture the feelings and notions associated with déjà vu simply by writing down the images that appeared during the experience. Later, he found that the memories had not vanished as before but could be brought back to a conscious level simply by reading the notes. The experience was brought back to him as if it was a conscious daydream . The striking implication here is that part of the conscious self, the I-function, is intimately involved and may be communicating with the processes of a déjà vu.
Perhaps to some, déjà vu is not worth its research weight in synapses. It may seem to many to be just an oddball, quirky brain trick that we learn to incorporate into our daily routine. Investigation into the implications of this neural event, however, seems to lead towards more in-depth knowledge of ourselves.
Quite a few of us who have "already-seen" would dare to see even more---would actually follow that dangerous, disappearing, inbound road consciously and witness for the first time what is usually jamais-vu and hidden, and I mean the steady dark frolic of neurons and the ghost that is called ego .
A better understanding of déjà vu may lead us closer to an understanding of the complex relationship between ourselves and our memories. It may light a path for a clearer view into how we incorporate ourselves into our memory and into how our memory is incorporated into our conscious selves. How can this be futile?